These traps position the file pointer.

• All registers not shown above are not used on entry and are preserved on exit.
• The value in D1.L is the absolute position requested for FS_POSAB/IOF_POSA and is the offset from the current position for FS_POSRE/IOF_POSR.
• If either trap returns with an off limits error then the pointer is set to the nearest limit (either 0 or the end of the file).
• By setting D1 to 0 and using FS_POSRE/IOF_POSR the current position of the file can be determined.
• In the case of FS_POSAB/IOF_POSA if the call is made for a direct sector access channel a special file position flag can be specified in D1. Using $F0FFF0FF returns the sector offset of the first physical sector of the current partition on multiple-partition devices (SMSQ v2.77+), otherwise D1 is unchanged.

The example below shows the use of FS_POSRE/IOF_POSR to find the current position in the file. It is assumed that A0 contains the channel ID.

pos     moveq   #fs_posre,d0    ; $43
        moveq   #0,d1           ; To find the current position
        moveq   #-1,d3          ; Timeout
        trap    #3              ; The current position is now in D1.L
        tst.l   d0              ; OK? . .
        bne     error           ; . . no!